Removing a seatpost which is stuck in a frame can be one of the most
difficult and challenging jobs that may come your way.
These tips should help you meet this challenge, and emerge victorious.

Prevention

To update an old saying, 28 grams of prevention are worth 454 grams of cure. Stuck seatposts are always the result of improper installation. If you do it right, you will never have a seatpost get stuck after you install it.

Always use grease. [Not for carbon-fiber seatposts, which easily can be damaged by seatpost clamps, too. For a carbon-fiber seatpost, see suggestions later on this page -- John Allen] The inside of the seat tube should be heavily coated with grease all the way 'round before you install the seatpost.If you use enough grease in the seat tube, there is no need to grease the seatpost itself. (When you make a peanut butter sandwich, you only need to put the peanut butter on one of the slices of bread.)

The three rules of hammering seatposts:

Never install a seatpost with a hammer.

Never, never install a seatpost with a hammer.

Never, never, EVER install a seatpost with a hammer!

Do not install a plain "pipe-type" seatpost without having a saddle attached to it. They can slip down too far and get stuck where you can't reach them.

Diagnosis

Before you get serious about a stuck seatpost, you should find why it is stuck. There are two possible reasons: The seatpost may be stuck mechanically, for instance by being the wrong size and having been forced in; or, the problem may be chemical, caused by corrosion.

If an oversized seatpost was forced into the frame, it will often make a noticeable bulge in the seat tube. Even if you cannot see this bulge, you can sometimes feel it by running your fingers up and down the seat tube about where you would expect the seat post to end.

If a thin-walled seatpost has been deformed (out-of-round) by overtightening the seatpost bolt, this will usually be visible where the seatpost emerges from the seat tube. If the seatpost is out-of-round, you should not expect to be able to get it to turn more than a few degrees from side-to-side. If you force it too far rotationally, you may jam it in even worse.

Cure

Do not try to remove a seatpost by pulling on it with a pipe wrench, locking pliers or any other tool. Instead, use a saddle. Nothing gets as good a grip on a seatpost as a saddle, because it has the hardware designed specifically for the purpose. If you are worried about damaging a good saddle, use one of the yellow BMX saddles you have in the cellar.

At the first sign of difficulty in moving a seatpost, remove the seatpost bolt completely, don't just loosen it. Sometimes this is all that it will take.

The next thing to try is prying the ears of seat lug apart slightly with a screwdriver. [Only with a steel frame, though. This can permanently damage an aluminum or carbon-fiber frame. -- John Allen] Sometimes it is easiest to stick a flat-bladed screwdriver between the ears and twist gently. Other times you may have better luck by inserting a large Phillips head screwdriver or Allen wrench into the bolt hole on one ear at a time and bending the two sides individually.

Most repairs are easier if the bike is held in a workstand, and for some jobs it is helpful to have the bike partially disassembled. This is not the case with seatpost extraction.

It is easiest to work with a fully assembled bike, sitting on the floor on its own tires. When pulling on the seatpost, the best way to hold the bike down is to put a foot on a pedal.

[The moving parts of a suspension seatpost are definitely not as strong as a single steel tube or forging. You will have to clamp a suspension seatpost below the suspension. -- John Allen].

You can get the best purchase by standing behind the saddle, with your legs straddling the rear wheel. It may be helpful to have an assistant hold the front end of the bike steady. Even if you don't use an assistant, the front wheel should be restrained from turning from side-to-side. This may be done with a commercial handlebar clamping tool, or by strapping the wheel against the downtube with a toe strap.

For the most recalcitrant cases, if the seatpost has a one-piece saddle clamp, you can mount the top of the seatpost in a vise, then twist and pull the bike or frame. If you have an assistant handy, have one of you apply the force in a rotational direction, while the other applies force to pull the frame away from the seatpost.

Unfortunately, many seatposts will not lend themselves to this approach, because the saddle clamp may be pressed or bonded to the tubular part of the seatpost, and the joint isn't designed to withstand such force.

Normally, it is best to raise and lower seatposts straight up or down, without twisting them, because twisting can cause unsightly scratches on the seatpost. This does not apply when you are dealing with badly stuck post, however. With stuck seatposts, your first priority should be to try to turn the seatpost, even if it won't move vertically. You can apply much more effective force rotationally than you can vertically, and if you can get the post to turn, victory is in sight. Once you can turn the seatpost, you can run oil in between it and the seat tube, and the twisting action will distribute the oil, completely freeing the post.

[You could clamp the tube of the seatpost in a vise, but you will ruin it unless you have cylindrical clamp blocks that fit it. Deforming the seatpost could damage the frame too and jam the seatpost in tighter, so clamp it up high. Other possibilities, once you have decided to sacrifice the seatpost, are to drill a hole through it for a bar, or to bend it over, being careful not to damage the frame. If you've drilled the seatpost for a bar, you might try pounding the seatpost out as well as twisting it-- John Allen]

For steel seatposts stuck into steel frames, where the problem is often caused by rust, penetrating oil can do wonders. If you don't have real penetrating oil, any light lubricating oil is better than nothing, but penetrating oil is made specifically for this purpose, and you should buy a can if you don't already have one.

Aluminum seatposts frequently become stuck by corrosion also, and penetrating oil is almost useless against aluminum oxide. Fortunately, aluminum oxide can be dissolved like magic by using ammonia. [Jobst Brandt doesn't think this works, because the ammonia won't penetrate -- see his comments on stuck handlebar stems. Drano drain cleaner in water also dissolves aluminum oxide. Leaving the frame upside down with the seatpost soaking in one of these liquids may possibly free the seatpost. With the frame upside down, you might also run liquid down from inside as described in additional suggestions.-- John Allen]

[Temperature-differential method, which is applicable to any seatpost material: Buy dry ice (solid carbon dioxide, which melts at -78.5° C (- 108° F). If you have access to laboratory supplies, you might also use liquid nitrogen, which is even colder, though its cooling effect is not as great because it boils, forming a shield of gas around itself. Ordinary water ice also might work. Remove the bottom-bracket parts, cork the top of the seatpost if it is open, and with the frame upside-down and a saddle attached to the seatpost, drop chips of (dry) ice or pour liquid nitrogen down the seat tube into the seatpost. Then hold the saddle down on the floor with your feet and twist the frame. You may also warm the seat tube by pouring hot water onto its outside. Wear waterproof winter gloves and boots and socks. Do not touch dry ice, the seatpost or other parts chilled by dry ice or liquid nitrogen, and odn't let them spill on you. I thank John Newgard for this suggestion. Sheldon's original suggestion follows -- John Allen]

If nothing else works to free up a steel or titanium seatpost, the next-to-last resort is to heat the seat tube up with a hair dryer or propane torch. This should be done with great care so as not to do too much damage to the paint. You should work as fast as you safely can, because you want to heat the seat tube so that it will expand, but if possible you should quickly put the torch down and start pulling on the saddle before the heat works its way through the seat tube and makes the seatpost expand too.

The torch technique is worse than useless when you are dealing with an aluminum seatpost stuck in a steel or titanium frame, because aluminum expands twice as much as steel, and 2 1/2 times as much as titanium for the same increase in temperature. In fact, the exact opposite technique will often do the trick for aluminum seatposts -- cool the seatpost down as rapidly as possible. The contents of a CO2 tire inflation cartridge applied inside the seatpost can shrink it down just enough to do the trick. [As will dry ice, which is also CO2, and can get the seatpost colder-- John Allen]

If nothing else works, the final resort is the old hacksaw blade trick. Cut the seatpost off so that about 1/2" is left sticking out, then insert a hacksaw blade into the seatpost and carefully cut a slit in the post. This is very laborious, and you run the risk of damaging the frame if you cut too far, but this approach cannot fail. Once you have cut the slit, grab one edge of the cut with a locking plier and roll the seatpost up inside itself and pull it out.

NEW! Suggestions for carbon fiber frames and seatposts by Witold Walkwski, with interpolated comments by John Allen.

I bought recently a used Kuota Kalibur carbon frame with carbon post. The post got stuck in the frame while being shipped by Fedex. Both the post and seat tube are not round but with a drop shape profile so you cannot even turn it. I tried to lubricate the post with soapy water and with oil. [Bad idea: oil expands the resin binder of the composite material and can deteriorate it.] I installed a piece of steel rod in the seat rail clamp, inverted the bike, stood over the inverted bike, stepped on the bar with both feet and pulled on the frame with all the force I had. Nothing happened. Tried to warm up the frame by friction (rubbing with clean soft cloth). Wiggled the post. Not even a sign of improvement. Then I have studied all the posts on the web in this matter. Tried the same exercises again, with zero results, except some pain in my back. Then I confronted the situation, that the only option left would be to cut out the post with a long straight blade which is absolutely crazy and risky on the carbon frame.

Then I stepped back to my engineering thinking (for last 20 years I design and build special prototype machinery). First I checked on the heating / cooling options and found that the thermal expansion of carbon epoxy composites is only 0.000001/F which makes it one of the materials with absolutely best thermal stability - forget about heating or cooling carbon - it will not help and may only damage the frame.

Then I started to analyze the physics of pulling one composite tube out of another. I was sure it was not glued together, as the frame is old enough to be perfectly cured and the tube was there only for a few weeks. It was only held there by friction. It was not inserted with a lot of force so it must have created some mechanism that locks the pieces together. My further conclusion was that if you pull on the frame trying to pull out the post you are causing the seat tube to elongate, which in turn reduces its diameter and causes even tighter clamping on the post. The more force you apply pulling on the seat tube, the It is exactly what happens when you put one piece of plastic tubing in another piece of tubing and then try to pull it out. [like a Chinese finger puzzle -- John Allen]

The best way to do it is not pulling on the outer tubing, but pushing the big tubing off the small tubing, just pressing on the edge of the outer tube while pulling on the end of the inner tube. Now I knew I would be able to do it. I only needed some way to apply reasonably large force just on the top edge of the seat tube. I took two aluminum plates that just fitted nicely between the seat rail clamp plate and the top of the seat tube (one plate on one side of the seat post and the other on the opposite), with the seat rail clamp screws extended by a few turns. Then I gently turned the rail clamp screws in and the seat post just came out without any struggle :) :) :) I did not apply any more force then, just slight finger pressure on the Allen key while turning the screws. I am sure that a similar method may be used on metal frames and seat posts or any combination of the material. You just need the right length of spacer blocks or some kind of screw attachment to do the pushing off the seat tube from the seat post.

Drastic solution, contributed by Matt Duff: Sodium Hydroxide - AKA Caustic Soda. ONLY FOR AN ALUMINUM SEATPOST IN A STEEL FRAME AS FAR AS I KNOW. It will destroy an aluminum frame. It won't affect steel, and as far as I know it won't affect most plastics.

DISCLAIMER - don't attempt if you are unsure about anything and always use thick rubber gloves, face mask, overalls, boots. Sodium hydroxide will eat away at the aluminium but it will also eat off your skin faster than anything. [Getting it in the eyes can cause blindness. See precautions here. Have a source of running water, and for good measure, a bucket of water ready, in case of an accident.-- John Allen]

PREPARE THE BIKE:

Saw off the seat post at the top of the tube and bung it up with something plastic. You must do this because otherwise, liquid would flow out when the caustic soda eats through the seatpost).Make sure it is liquid tight.Remove bottom bracket. To avoid blowing out caustic lye under pressure when you pull things apart later, there must be a way for gas to get out -- generally, through the bottom bracket. I'd suggest removing anything else off the bike that is aluminium, and covering up any decals you may want to save. Take the bike outside and set upside down on a patch of dirt away from kids and animals.

PREPARE THE SODIUM HYDROXIDE:

Measure out 200g of sodium hydroxide powder into a plastic cup. Fill a 750ml bottle with 500ml of cool water.

Put on all the safety gear - the mix will get hot, produce fumes, and may splash. Don't let it touch your skin!

Place the bottle of water into an empty plastic bucket - the bottle may overflow so you want to catch that stuff. Slowly pour the 400g of powder into the 750ml bottle - use a thin wooden stick to stir it. It will get hot - make sure there is no powder left in the bottom of the bottle.

POUR IT IN!

Using a funnel and a thin hose pour in a small amount of the liquid mix into the frame of the bike through the bottom bracket . Maybe about 100ml at a time - wait about 5 minutes and it will start bubbling and gas coming out. When it starts to slow down pour another 100ml in Continue this so that the liquid is in the bike tube for about 1 hour. [No fire or flame nearby -- caustic soda releases hydrogen gas when it reacts with aluminum. -- John Allen].

CLEAN UP:

Break the seal on the seatpost hole - warning! lots of liquid will come out. Be covered up and check where it is all going to flow to. Run fresh water through the frame thoroughly to make sure it is all out Clean the area - dilute any that is on the ground with lots and lots of water Throw away any containers and wash tools really really well

I found I had to do this twice. The second time I had to plug the top tube to stop the liquid flowing down there. [You might tilt the frame so liquid will not run down the top tube -- John Allen] Finally all that was left was a thin sliver of seat post. Hope this is good information. Cheers!